"In psychology and behavioral economics, the endowment effect (also known as divestiture aversion and related to the mere ownership effect in social psychology) is the hypothesis that people ascribe more value to things merely because they own them.
This is typically illustrated in two ways. In a valuation paradigm, people will tend to pay more to retain something they own than to obtain something they do not own—even when there is no cause for attachment, or even if the item was only obtained minutes ago. In an exchange paradigm, people given a good are reluctant to trade it for another good of similar value. For example, participants first given a Swiss chocolate bar were generally unwilling to trade it for a coffee mug, whereas participants first given the coffee mug were generally unwilling to trade it for the chocolate bar."

This doesn't seem to exactly fit the subforum, but it seems the most sciency of all the forums.

Basically I think it's interesting that there is an underlying psychological theory of why fan trade proposals are so terrible and why trades in general are much rarer than they probably out to be.